Conversion of Fischer-Tropsch oxygenates to middle distillate

ABSTRACT

Water soluble oxygenates of Fischer-Tropsch synthesis separated from water and acids are sequentially converted by a dehydration catalyst and a special zeolite catalyst to provide a product containing a major proportion of middle distillate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of processes for convertingoxygenate by-products from the Fischer-Tropsch synthesis to usefulhydrocarbon products, particularly, middle distillate.

2. Description of the Prior Art

The conversion of oxygenated organic compounds to hydrocarbons has beenthe subject of numerous prior-art disclosures. U.S. Pat. No. 3,928,483discloses a process for the production of aromatic rich gasoline boilingrange hydrocarbons from lower alcohols such as methanol, ethanol,propanol and corresponding ethers. In this patent, the process iscarried out in two or more stages wherein the alcohol or ether iscontacted with a condensation catalyst to produce aliphatic dehydrationproducts and water. The dehydration product is thereafter converted togasoline boiling hydrocarbon by contact with a special crystallinealuminosilicate zeolite providing a silica-to-alumina ratio greater than12, a constraint index within the range of 1 to 12 and a dried crystaldensity of not less than about 1.6 grams per cubic centimeter. A ZSM-5crystalline zeolite is representative of the special class of zeoliteproviding the above defining characteristics. U.S. Pat. No. 3,907,915 isdirected to the conversion of aliphatic carbonyl containing compoundswith the special zeolite above defined. U.S. Pat. No. 3,998,898 isdirected to converting a mixture of a difficult to convert aliphaticorganic compound in combination with easily converted aliphaticalcohols, esters, acetals and analogs thereof over the specialcrystalline zeolite above defined to produce highly aromatic gasolinehydrocarbons and light aliphatic hydrocarbons.

SUMMARY OF THE INVENTION

The present invention is directed to an improved method and combinationof processing steps for converting a wide spectrum of water solubleoxygenated products such as those obtained from a Fischer-Tropschoperation to middle distillate hydrocarbon products. The term "middledistillate" as used herein shall be understood to refer to hydrocarbonfractions whose boiling points at a pressure of one atmosphere lie inthe mid-range, generally considered to be from about 300° F. to as highas about 800° F., and includes such products as jet fuel, diesel fuel,furnace fuel, industrial fuel and kerosene.

The improved process of this invention generally involves collecting andpassing the mixed water soluble oxygenates of a Fischer-Tropsch syngasconversion operation comprising alcohols, ethers, aldehydes, ketones,acids and water after separation of acids and some water in contact witha dehydration catalyst under conditions to achieve at least 25%dehydration conversion of the feed and thereafter processing all or apart of the product of dehydration over a special crystallinealuminosilicate defined below to produce a complex mixture of productscomprising a minor amount of gases and high octane C₅ ⁺ gasoline and amajor amount of middle distillate boiling range hydrocarbons. In thiscombination operation, the dehydration of the charged oxygenates isimportant and effected under conditions to achieve an elevatedconversion level normally falling short of complete conversiondehydration of the oxygenates. Thereafter a water phase containingunconverted oxygenates is separated from a water insoluble phasecomprising dehydrated oxygenates. This water insoluble phase comprises amixture of gaseous products, for the most part light olefins, and mayalso contain a relatively minor amount of liquid C₆ ⁺ organic materialsmade up largely of dehydration products of aldehydes and ketones. Thewater phase containing unreacted oxygenates is recycled to the primarydistillation zone upstream of the dehydration zone. The substantiallywater-free dehydrated oxygenates, preferably from which the C₆ ⁺dehydration products have been previously removed, are thereafterconverted by a special zeolite catalyst herein described in a separatezeolite catalytic conversion zone.

The combination process of the invention achieves significant advantagesat least with respect to the zeolite catalyst life by substantiallyreducing the amount of water and unconverted oxygenates contacting thezeolite catalyst. The special zeolite catalytic conversion of thewater-feee dehydrated oxygenates is more efficient, since quenching ofthe zeolite catalyst conversion operation is virtually eliminated.

The processing combination of the invention is particularly concernedwith processing C₂ ⁺ oxygenates of a Fischer-Tropsch syngas conversionoperation and dehydration products thereof. The significant advantagesof the processing combination reside in operating the middle distillateforming stage independently of the initial dehydration state, and anyunconverted (dehydrated) oxygenates can be separated and recycled to thedistillation operation upstream of the dehydration zone and/or to thezeolite catalytic conversion zone. Where maximum conversion ofdehydrated oxygenates to middle distillate is desired, any gasolinepresent in the effluent from the zeolite catalytic conversion zone canbe separated therefrom and recycled to this zone together with freshdehydrated oxygenates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The crystalline aluminosilicate component used is a special crystallinezeolite such as ZSM-5 zeolite which is characterized by a pore dimensiongreater than about 5 Angstroms, i.e., it is capable of sorbingparaffins, it has a silica-to-alumina ratio of at least 12 and aconstraint index within the range of 1 to 12. Zeolite A, for example,with a silica-to-alumina ratio of 2.0, is not useful in this invention,and it has no pore dimension greater than about 5 Angstroms.

The crystalline aluminosilicates herein referred to, also known aszeolites, constitute an unusual class of natural and synthetic minerals.They are characterized by having a rigid crystalline framework structurecomposed of an assembly of silicon and aluminum atoms, each surroundedby a tetrahedron of shared oxygen atoms, and a precisely defined porestructure. Exchangeable cations are present in the pores.

The zeolites utilized herein exhibit some unusual properties. They arevery active even with silica-to-alumina ratios exceeding 30. Thisactivity is surprising, since catalytic activity of zeolites isgenerally attributed to framework aluminum atoms and cations associatedwith these aluminum atoms. These zeolites retain their crystallinity forlong periods in spite of the presence of steam even at high temperatureswhich induce irreversible collapse of the crystal framework of otherzeolites, e.g., of the X and A type. Furthermore, carbonaceous deposits,when formed, may be removed by burning at higher than usual temperaturesto restore activity. In many environments the zeolite of this classexhibit very low coke forming capability, conducive to very long timeson stream between burning regenerations.

An important characteristic of the crystal structure of this class ofzeolites is that it provides constrained access to, and egress from, theintracrystalline free space by virtue of having a pore dimension greaterthan about 5 Angstroms and pore windows of about a size such as would beprovided by 10-membered rings of oxygen atoms. It is to be understood,of course, that these rings are those formed by the regular dispositionof the tetrahedra making up the anionic framework of the crystallinealuminosilicate, the oxygen atoms themselves being bonded to the siliconor aluminum atoms at the centers of the tetrahedra. Briefly, thepreferred zeolites useful in this invention have a silica-to-aluminaratio of at least about 12 and a structure providing constrained accessto the crystalline free space.

The silica-to-alumina ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with a silica-to-aluminaratio of at least 12 are useful, it is preferred to use zeolites havinghigher ratios of at least about 30. Such zeolites, after activation,acquire an intracrystalline sorption capacity for normal hexane which isgreater than that for water, i.e., they exhibit "hydrophobic"properties. It is believed that this hydrophobic character isadvantageous in the present invention.

The zeolites useful as catalysts in this invention freely sorb normalhexane and have a pore dimension greater than about 5 Angstroms. Inaddition, their structure must provide constrained access to some largermolecules. It is sometimes possible to judge from a known crystalstructure whether such constrained access exists. For example, if theonly pore windows in a crystal are formed by 8-membered rings of oxygenatoms, then access by molecules of larger cross-section than normalhexane is substantially excluded and the zeolite is not of the desiredtype. Zeolites with windows of 10-membered rings are preferred, althoughexcessive puckering or pore blockage may render these zeolitessubstantially ineffective. Zeolites with windows of 12-membered rings donot generally appear to offer sufficient constraint to produce theadvantageous conversions desired in the instant invention, althoughstructures can be conceived, due to pore blockage or other cause, thatmay be operative.

Rather than attempt to judge from crystal structure whether or not azeolite possesses the necessary constrained access, a simpledetermination of the "constraint index" may be made by continuouslypassing a mixture of equal weight of normal hexane and 3-methylpentaneover a small sample, approximately 1 gram or less, of zeolite atatmospheric pressure according to the following procedure. A sample ofthe zeolite, in the form of pellets or extrudate, is crushed to aparticle size about that of coarse sand and mounted in a glass tube.Prior to testing, the zeolite is treated with a stream of air at 1000°F. for at least 15 minutes. The zeolite is then flushed with helium andthe temperature adjusted between 550° F. and 950° F. to give an overallconversion between 10% and 60%. The mixture of hydrocarbons is passed at1 liquid hourly space velocity (i.e., 1 volume of liquid hydrocarbon pervolume of catalyst per hour) over the zeolite with a helium dilution togive a helium to total hydrocarbon mole ratio of 4:1. After 20 minuteson stream, a sample of the effluent is taken and analyzed, mostconveniently by gas chromatography, to determine the fraction remainingunchanged for each of the two hydrocarbons.

The "constraint index" is calculated as follows: ##EQU1##

The constraint index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Catalysts suitable for the presentinvention are those which employ a zeolite having a constraint indexfrom 1.0 to 12.0. Constraint Index (C.I.) values for some typicalzeolites, including some not within the scope of this invention, are:

    ______________________________________                                        CAS                 C.I.                                                      ______________________________________                                        Erionite            38                                                        ZSM-5               8.3                                                       ZSM-11              8.7                                                       ZSM-35              6.0                                                       TMA Offretite       3.7                                                       ZSM-38              2.0                                                       ZSM-12               2                                                        Beta                0.6                                                       ZSM-4               0.5                                                       Acid Mordenite      0.5                                                       REY                 0.4                                                       Amorphous Silica-alumina                                                                          0.6                                                       ______________________________________                                    

The above-described Constraint Index is an important, and even critical,definition of those zeolites which are useful to catalyze the instantprocess. The very nature of this parameter and the recited technique bywhich it is determined, however, admit of the possibility that a givenzeolite can be tested under somewhat different conditions and therebyhave different constraint indexes. Constraint Index seems to varysomewhat with severity of operation (conversion). Therefore, it will beappreciated that it may be possible to so select test conditions toestablish multiple constraint indexes for a particular given zeolitewhich may be both inside and outside the above defined range of 1 to 12.

Thus, it should be understood that the parameter and property"Constraint Index" as such value is used herein is an inclusive ratherthan an exclusive value. That is, a zeolite when tested by anycombination of conditions within the testing definition set forthhereinabove to have a constraint index of 1 to 12 is intended to beincluded in the instant catalyst definition regardless that the sameidentical zeolite tested under other defined conditions may give aconstraint index value outside of 1 to 12.

The class of zeolites defined herein is exemplified by ZSM-5, ZSM-11,ZSM-12, ZSM-21, and other similar materials. U.S. Pat. No. 3,702,886describing and claiming ZSM-5 is incorporated herein by reference.

ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, theentire contents of which are incorporated herein by reference.

ZSM-12 is more particularly described in U.S. Pat. No. 3,832,449, theentire contents of which are incorporated herein by reference.

Abandoned U.S. patent application Ser. No. 358,192, filed May 7, 1973,the entire contents of which are incorporated herein by reference,describes a zeolite composition designated as ZSM-21, and a method ofmaking such, which is useful in this invention. There is evidence whichsuggests that this composition may be composed of at least two differentzeolites, designated ZSM-35 and ZSM-38, one or both of which are theeffective material insofar as the catalysis of this invention isconcerned. Either or all of these zeolites is considered to be withinthe scope of this invention. ZSM-35 is described in U.S. Pat. No.4,016,265 and ZSM-38 is described in U.S. Pat. No. 4,046,859.

The specific zeolites described, when prepared in the presence oforganic cations, are substantially catalytically inactive, possiblybecause the intracrystalline free space is occupied by organic cationsfrom the forming solution. They may be activated by heating in an inertatmosphere at 1000° F. for 1 hour, for example, followed by baseexchange with ammonium salts, followed by calcination at 1000° F. inair. The presence of organic cations in the forming solution may not beabsolutely essential to the formation of this special type zeolite;however, the presence of these cations does appear to favor theformation of this special type of zeolite. More generally, it isdesirable to activate this type zeolite by base exchange with ammoniumsalts, followed by calcination in air at about 1000° F. for from about15 minutes to about 24 hours.

Natural zeolites may sometimes be converted to this type zeolite byvarious activation procedures and other treatments such as baseexchange, steaming, alumina extraction and calcination, alone or incombinations. Natural minerals which may be so treated includeferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulanditeand clinoptilolite. The preferred crystalline aluminosilicates areZSM-5, ZSM-11, ZSM-12 and ZSM-21, with ZSM-5 in the acid form, i.e.,H-ZSM-5, being particularly preferred.

In a preferred aspect of this invention, the initial zeolites useful ascatalysts herein are selected as those having a crystal frameworkdensity, in the dry hydrogen form, of not substantially below about 1.6grams per cubic centimeter. It has been found that zeolites whichsatisfy all three of these requirements are most desired. Therefore, thepreferred catalysts of this invention are those comprising zeoliteshaving a constraint index as defined above of about 1 to 12, asilica-to-alumina ratio of at least about 12 and a dried crystal densityof not substantially less than about 1.6 grams per cubic centimeter. Thedry density for known structures may be calculated from the number ofsilicon plus aluminum atoms per 1000 cubic Angstroms, as given e.g. onpage 19 of the article on "Zeolite Structure" by W. M. Meier. Thispaper, the entire contents of which are incorporated herein byreference, is included in "Proceedings of the Conference on MolecularSieves, London, April 1967", published by the Society of ChemicalIndustry, London, 1968. When the crystal structure is unknown, thecrystal framework density may be determined by classical pycnometertechniques. For example, it may be determined by immersing the dryhydrogen form of the zeolite in an organic solvent which is not sorbedby the crystal. It is possible that the unusual sustained activity andstability of this class of zeolites are associated with its high crystalanionic framework density of not less than about 1.6 grams per cubiccentimeter. This high density of course must be associated with arelatively small amount of free space within the crystal, which might beexpected to result in more stable structures. This free space, however,seems to be important as the locus of the catalytic activity.

Crystal framework densities of some typical zeolites, including somewhich are not within the purview of this invention, are:

    ______________________________________                                                        Void        Framework                                         Zeolite         Volume      Density                                           ______________________________________                                        Ferrierite      0.28 cc/cc  1.76 g/cc                                         Mordenite       .28         1.7                                               ZSM-5, -11      .29         1.79                                              Dachiardite     .32         1.72                                              L               .32         1.61                                              Clinoptilolite  .34         1.71                                              Laumontite      .34         1.77                                              ZSM-4 (Omega)   .38         1.65                                              Heulandite      .39         1.69                                              P               .41         1.57                                              Offretite       .40         1.55                                              Levynite        .40         1.54                                              Erionite        .35         1.51                                              Gmelinite       .44         1.46                                              Chabazite       .47         1.45                                              A               .5          1.3                                               Y               .48         1.27                                              ______________________________________                                    

Table 1 below identifies a typical oxygenated product stream of aFischer-Tropsch syngas conversion operation.

                  TABLE 1                                                         ______________________________________                                        Oxygenated Product of Fischer-Tropsch Synthesis                               Components             wt. %                                                  ______________________________________                                        Water                  15.0                                                   Acetaldehyde           2.4                                                    Methanol               5.1                                                    Ethanol                44.3                                                   Acetone + C.sub.3 Aldehyde                                                                           12.2                                                   Isopropanol            3.8                                                    Propanol               6.2                                                    Methyl Ethyl Ketone + C.sub.4 Aldehyde                                                               4.0                                                    Butanol                 .5                                                    2-Methyl-1-propanol     .5                                                    C.sub.5 Ketones        1.0                                                    1-Butanol              2.9                                                    C.sub.5 Alcohols       1.5                                                    C.sub.6 + Oxygenates    .4                                                                           99.8                                                   ______________________________________                                    

Table 2 below identifies the boiling points of the major oxygenatedcomponents of the charge materials and their dehydration products. Itwill be noted from Table 2 that at the indicated "Proposed Cut Point"the unconverted portion of the charge will separate with the water phaseand the dehydration product may be separated as vaporous material from aseparation zone maintained under the identified temperature and pressureconditions. This vapor/liquid separation operation is maintainedindependent of the initial reactor dehydrating operating conditions.

                  TABLE 2                                                         ______________________________________                                         Boiling Point at 100 PSIA                                                    ______________________________________                                        Ethylene        -79.9° F.                                              Propylene       42.3                                                          Dimethyl Ether  70.0                                                          Butene          133.                                                          Acetaldehyde    168.                                                          Pentene         212.                                                                          Proposed Cut Point                                            Propionaldehyde 246.                                                          Methanol        252.                                                          Acetone         258.                                                          Ethanol         276.                                                          Isopropanol     281.                                                          Hexene          284.                                                          n-Propanol      318.                                                          Methyl Ethyl Ketone                                                                           322.                                                          Water           328.                                                          ______________________________________                                    

The drawing is a schematic showing of the processing arrangement of thisinvention comprising a primary distillation zone, a dehydration zone, adehydrated product separation zone, a zeolite catalytic conversion zoneand a product separation zone.

Referring now to the drawing by way of example, a stream of oxygenatedproducts and water separated from the product of a Fischer-Tropschsyngas conversion operation is charged to the process of this inventionby conduit 2 to a distillation column or zone 3 maintained at atemperature and a pressure selected to achieve separation of water andacids from the remaining oxygenates. In distillation zone 3, aseparation is made in the presence of relatively large amounts of water,a water phase and acids withdrawn from the bottom of the zone by conduit4, with the remaining oxygenates and water being recovered from the topthereof by conduit 5. The oxygenates and water in conduit 5 are heatedin heat exchanger 6 to an elevated temperature within the range of about600° to 1100° F. and preferably about 900° F. before being passed incontact with a dehydrating catalyst in dehydration zone 7. A portion ofthe material in conduit 5 may be passed to vent as shown when required.In dehydration zone 7, the oxygenates and retained water are passed incontact with a dehydration catalyst suitable for the purpose. Any of themany dehydration catalysts known in the art can be used herein withgamma alumina being preferred. Dehydration zone 7 is maintained undertemperature conditions which will achieve a high conversion of theoxygenates to a dehydrated product suitable for passing upon recovery incontact with the middle distillate forming special zeolite catalyst.Table 3 below identifies conditions which may be employed to achieve adesired conversion to dehydrated oxygenates preferably to within therange of 25 to 100%.

                  TABLE 3                                                         ______________________________________                                        Endothermic Heats of Dehydration at 700° F.                            Alcohol → Olefin + Water                                               Alcohol      - H Kcal/Mole                                                                              - H cal/gm                                          ______________________________________                                        Ethanol      11.20        243                                                 n-Propanol   8.93         149                                                 i-Propanol   12.15        203                                                 n-Butanol.sup.1                                                                            5.37          72                                                 n-Pentanol.sup.2                                                                           4.19          48                                                 n-Hexanol.sup.3                                                                            4.31          42                                                 ______________________________________                                        Estimated Adiabatic Temperature Drop                                          For 900° F. Inlet                                                      Charge         Mole                                                           Composition    %                                                              ______________________________________                                        Ethanol        84.3                                                           n-Propanol     8.3                                                            i-Propanol     3.0                                                            n-Butanol      3.4                                                            n-Pentanol     1.0                                                            ______________________________________                                        Conversion     .sup.T Adiabatic                                               %              °F.                                                     ______________________________________                                        100            420                                                            50             575                                                            25             745                                                            ______________________________________                                         .sup.1 Olefin product taken as t2-butene                                      .sup.2 Olefin product taken as 2M--2butene                                    .sup.3 Olefin product taken as 2M--2pentene                              

The product of the dehydration operation and comprising dehydratedoxygenates, water and unconverted oxygenates (not dehydrated) is passedby conduit 8 to a separation zone 9 maintained at a selected temperatureand pressure designed to achieve a separation of dehydration productcommensurate with a separation shown, for example, by Table 2 above.Thus, a separation is made in zone 9 under selected temperature andpressure conditions which will achieve the recovery of water andunconverted oxygenates withdrawn by conduit 10 for recycle todistillation zone 3. In a preferred embodiment, the water insoluble C₆ ⁺dehydration products are withdrawn from zone 9 through conduit 11 where,if desired, they may be conveyed to a gasoline conversion unit. Thepresence of these C₆ ⁺ dehydration products in the feed to the zeolitecatalytic conversion zone where the middle distillate is to be used asdiesel fuel is undesirable since these products tend to undergoconversion in this zone to aromatic compounds which result in a lowercetane number for the diesel fuel. Separation of water from unconvertedoxygenates before recycle is not essential. Light olefins and otherdehydration products such as herein identified are recovered fromseparation zone 9 by conduit 12 for passage to heater 13 wherein thetemperature of the light olefin stream is raised before contacting thespecial zeolite catalyst herein identified in zone 14. In zone 14, thetemperature is maintained within the range of from about 300° F. toabout 800° F., preferably from about 350° F. to about 600° F., apressure within the range of from about 100 psig to about 2,000 psig,preferably from about 500 psig to about 1,000 psig, and an LHSV (LiquidHourly Space Velocity) of from about 0.2 to about 10 and preferably fromabout 0.5 to about 2. In this special zeolite catalyst contactingoperation, the light olefins and other products of dehydration areconverted to middle distillate and, smaller quantities of C₅ ⁺ gasoline.

The product of the zeolite catalyst conversion step is passed by conduit15 from zone 14 to a separator zone 16 wherein a separation is made torecover overhead vapor made up mostly of C₄ and lower boiling materialwhich is withdrawn through conduit 17 for recycle and/or through conduit19 for further conversion, e.g., in an alkylation zone, a polymerizationzone or a combination thereof, or for use as a fuel to satisfy part orall of the thermal requirements of the process. When used for recycle,it is contemplated passing all of the C₄ and lighter material throughconduit 18 to a compression zone 20 to raise the pressure thereinsufficient for recycle by conduit 21 and admixture with the dehydratedfeed in conduit 12 charged to heater 13 and/or for recycle by conduit 22and admixture with the oxygenated products stream in conduit 5 chargedto heater 6. The liquid stream recovered from separation zone 16 throughline 23 is conveyed to distillation zone 24 with the middle distillateproduct (330⁺ ° F.) being recovered through conduit 25 and the C₅ ⁺gasoline being recovered through conduit 26 for recycle through line 27and admixture with the dehydrated feed in conduit 12 and/or throughconduit 28 for use as such.

The following examples are further illustrative of the invention.

EXAMPLES 1-2

These examples illustrate the dehydration operation of the presentinvention as applied to feed streams similar to that of theFischer-Tropsch oxygenated product whose composition is given in Table1.

    ______________________________________                                                       Example 1                                                                             Example 2                                              ______________________________________                                        Dehydration                                                                   Conditions                                                                    °F.       704       852                                                PSIG             200       290                                                LHSV             3.3       2.1                                                % Conversion     18        91                                                 Selectivity to                                                                Hydrocarbons (wt %)                                                           Liquid*           0        26                                                 Gas              100       74                                                 Approximate                                                                   Composition of                                                                Gas (Wt %)                                                                    Ethylene          8        21                                                 Propylene        52        32                                                 Butylene         18        18                                                 Pentene           9         9                                                 C.sub.1-5 paraffins                                                                             2         6                                                 Unidentified     11        14                                                 ______________________________________                                         *In the preferred practice of the present invention, the liquid phase, if     present, is separated from the gaseous phase prior to introducing the         latter into the zeolite catalytic conversion zone.                       

EXAMPLES 3-4

These examples illustrate the conversion of dehydrated oxygenates tomiddle distillate and a relatively minor amount of C₅ -330° F. gasoline.The feed in both examples (passing through conduit 12) possessed thefollowing composition:

    ______________________________________                                        Component       Weight %                                                      ______________________________________                                        Ethane/Ethylene 0.1                                                           Propylene       27.8                                                          Propane         9.6                                                           Isobutane       22.5                                                          Butylenes       32.8                                                          n-Butane        6.2                                                           iso-+n-Pentane   .5                                                           Pentenes         .5                                                                           100.0                                                         ______________________________________                                    

The zeolite catalytic conversion zone was operated at about 600 psig andan LHSV of about 0.65 based on the olefin in the feed. The results wereas follows:

    ______________________________________                                                        Example 3                                                                             Example 4                                             ______________________________________                                        Days on stream °F.                                                                        1         15                                               reaction zone inlet                                                                             440       480                                               Weight % product based                                                        on olefin in feed                                                             C.sub.1-4 * Paraffins                                                                            1.4       1.4                                              Unreacted C.sub.3-4 olefins*                                                                    11.7      13.2                                              C.sub.5 - 330° F. gasoline**                                                              9.7      10.5                                              330° F..sup.+ middle distillate                                                          77.2      74.9                                                                100.0     100.0                                             ______________________________________                                         *Recyle to provide heat sink temperature control within the reaction zone     **Recycled to maximum conversion of feed to middle distillate. The            recycled gasoline was essentially 100% olefins.                          

Having thus generally described the method and processing combination ofthis invention and provided specific examples in support thereof, it isto be understood that no undue restrictions are to be imposed by reasonthereof except as defined by the following claims.

What is claimed is:
 1. A process for converting a mixture of C₂ pluswater soluble oxygenates comprising primarily a mixture of C₅ and lowerboiling alcohols, aldehydes, ketones and water to a product containing amajor proportion of middle distillate which comprises:(a) distilling theC₂ plus water soluble oxygenates to remove water and acids from amixture of C₅ and lower boiling alcohols, aldehydes and ketones; (b)dehydrating the mixture of C₅ and lower boiling alcohols, aldehydes andketones under conditions to achieve within the range of 25 to 100%conversion thereof to a dehydrated product containing eight olefins, (c)separating the dehydrated product from water and unconverted material,recycling the separated water and unconverted material to thedistillation step; and, (d) passing the dehydrated product in contactwith a special zeolite catalyst characterized by a pore opening of atleast 5 Angstroms, a silica-to-alumina ratio of at least 12 and aconstraint index within the range of 1 to 12, said contact between saiddehydrated product and said zeolite catalyst being effected at atemperature, pressure and Liquid Hourly Space Velocity sufficient toprovide a product containing a major proportion of middle distillate. 2.The process of claim 1 wherein the product of said zeolite catalystoperation is separated to provide a C₄ and lower boiling product from ahigher boiling product and separated lower boiling product is recycledto the zeolite catalyst conversion operation.
 3. The process of claim 1wherein the product of said zeolite catalyst operation is separated toprovide a C₅ ⁺ gasoline product and a middle distillate product andseparated C₅ ⁺ gasoline product is recycled to the zeolite catalystconversion operation.
 4. The process of claim 1 wherein the dehydratedproduct separated in step (c) contains a relatively minor amount of C₆ ⁺organic materials which are separated from said dehydrated product priorto passing the dehydrated product in contact with the special zeolitecatalyst in step (d).
 5. The process of claim 1 wherein the dehydrationcatalyst is gamma alumina.
 6. The process of claim 1 wherein the zeolitecatalyst is ZSM-5.
 7. The process of claim 1 wherein the dehydratedproduct is contacted with the special zeolite catalyst at a temperatureof from about 300° F. to about 800° F., a pressure of from about 100psig to about 2,000 psig and a Liquid Hourly Space Velocity of fromabout 0.2 to about
 10. 8. The process of claim 1 wherein the dehydratedproduct is contacted with the special zeolite catalyst at a temperatureof from about 350° F. to about 600° F., a pressure of from about 500psig to about 1,000 psig and a Liquid Hourly Space Velocity of fromabout 0.5 to about
 2. 9. A method for converting the water solubleoxygenates of a Fischer-Tropsch syngas conversion operation to a productcontaining a major proportion of middle distillate which comprises:(a)passing water soluble oxygenates comprising alcohols, aldehydes andketones separated from a water phase by distillation in contact with adehydration catalyst under conditions to obtain a dehydrated productcontaining light olefins; and, (b) passing the dehydrated product incontact with a zeolite catalyst providing a pore opening of at least 5Angstroms, a silica-alumina ratio of at least 12 and a constraint indexwithin the range of 1 to 12 and maintaining the temperature, pressureand Liquid Hourly Space Velocity conditions selective for the productionof a product containing a major proportion of middle distillate.
 10. Theprocess of claim 9 wherein the product of said zeolite catalystoperation is separated to provide a lower boiling product from a higherboiling product and separated lower boiling product is recycled to thezeolite catalyst conversion operation.
 11. The process of claim 9wherein the product of said zeolite catalyst operation is separated toprovide a C₅ ⁺ gasoline product and a middle distillate product andseparated C₅ ⁺ gasoline product is recycled to the zeolite catalystconversion operation.
 12. The process of claim 9 wherein the dehydratedproduct in step (a) contains a relatively minor amount of C₆ ⁺ organicmaterials which are separated from said dehydrated product prior topassing the dehydrated product in contact with the special zeolitecatalyst in step (b).
 13. The process of claim 9 wherein the dehydrationcatalyst is gamma alumina.
 14. The process of claim 9 wherein thezeolite catalyst is ZSM-5.
 15. The process of claim 9 wherein thedehydrated product is contacted with the special zeolite catalyst at atemperature of from about 300° F. to about 800° F., a pressure of fromabout 100 psig to about 2,000 psig and a Liquid Hourly Space Velocity offrom about 0.2 to about
 10. 16. The process of claim 9 wherein thedehydrated product is contacted with the special zeolite catalyst at atemperature of from about 350° F. to about 600° F., a pressure of fromabout 500 psig to about 1,000 psig and a Liquid Hourly Space Velocity offrom about 0.5 to about 2.